What is EMF?
EMF stands for Electromagnetic fields, it consists of electric and magnetic field.
Quote from WHO: Electric fields are created by difference in voltage: the higher the voltage, the stronger will be the resultant field. Magnetic fields are created when electric current flows: the greater the current, the stronger the magnetic field. An electric field will exist even when there is no current flowing. If current does flow, the strength of the magnetic field will vary with power consumption but the electric field strength will be constant.
How does EMF strength and effect correlate with AC/DC, voltage, current?
Quote from WHO:
EMF fields of different frequencies interact with the body in different ways, the higher the frequency the shorter the wavelength. Higher frequency (shorter wavelength) waves carry more energy than lower frequency (longer wavelength) fields. Some electromagnetic waves carry so much energy that they have the ability to break bonds between molecules. In the electromagnetic spectrum, gamma rays given off by radioactive materials, cosmic rays and X-rays carry this property and are called 'ionizing radiation'. Fields that are insufficient to break molecular bonds are called 'non-ionizing radiation'.
Electric Fields
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Magnetic Fields
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Electric fields arise from voltage. An electric field can be present even when a device is switched off.
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Magnetic fields arise from current flows. Magnetic fields exist as soon as a device is switched on and current flows.
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Strength is measured in Volts per meter (V/m)
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Strength is measured in amperes per meter (A/m). Commonly, EMF investigators use a related measure, flux density (in microtesla (µT) or millitesla (mT) instead.
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Field strength decreases with distance from the source.
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Field strength decreases with distance from the source.
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Most building materials shield electric fields to some extent.
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Magnetic fields are not attenuated by most materials.
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Quote from Canadian Electricity Association:
EMF is dependent upon line voltage, loads and current in a power line. The fields are highest directly under/over the power line and quickly become weaker as one moves away from the center line.
Earth does produce static magnetic field of strengths up to 500 mG. Since these are DC or static fields, their potential interaction with the human body would be different (as compare to AC fields).
Static electric and magnetic fields associated with DC transmission lines are not viewed as a health concern. Their levels are very low and similar to the naturally occurring static fields we are exposed to in our daily lives.
Quote from Atco Electric: The Difference Between AC and DC Fields. The modern electric power system operates using alternating current (AC) almost exclusively. AC changes polarity or “cycles” 60 times a second. Its fields also cycle at 60 Hz and are referred to as Extremely Low Frequency (ELF) fields. Direct current (DC) is constant, like current from a battery. Its electric and magnetic fields are also constant (frequency of zero) and are referred to as static fields.
Quote from Japan EMF Information Center:
How does EMF strength and effect correlate with distance?
Quote from WHO:
Typical electric field strengths measured near household appliances (at a distance of 30 cm):
Electric appliance
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Electric field strength (V/m)
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Stereo receiver
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180
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Iron
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120
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Refrigerator
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120
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Mixer
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100
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Toaster
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80
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Hair dryer
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80
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Color TV
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60
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Coffee machine
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60
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Vacuum cleaner
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50
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Electric oven
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8
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Light bulb
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5
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Guideline limit value of 5000 V/m.
Typical magnetic field strength of household appliances at various distances
Electric appliance
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3 cm distance (µT)
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30 cm distance (µT)
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1 m distance (µT)
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Hair dryer
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6 – 2000
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0.01 – 7
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0.01 – 0.03
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Electric shaver
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15 – 1500
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0.08 – 9
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0.01 – 0.03
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Vacuum cleaner
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200 – 800
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2 – 20
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0.13 – 2
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Fluorescent light
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40 – 400
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0.5 – 2
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0.02 – 0.25
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Microwave oven
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73 – 200
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4 – 8
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0.25 – 0.6
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Portable radio
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16 – 56
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1
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< 0.01
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Electric oven
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1 – 50
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0.15 – 0.5
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0.01 – 0.04
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Washing machine
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0.8 – 50
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0.15 – 3
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0.01 – 0.15
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Iron
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8 – 30
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0.12 – 0.3
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0.01 – 0.03
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Dishwasher
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3.5 – 20
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0.6 – 3
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0.07 – 0.3
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Computer
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0.5 – 30
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< 0.01
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Refrigerator
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0.5 – 1.7
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0.01 – 0.25
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<0.01
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Colour TV
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2.5 - 50
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0.04 – 2
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0.01 – 0.15
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Guideline limit for the general public of 100 µT.
Quote from Atco Electric:
MRI machines
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1.4-4 million µT
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Battery operated appliances
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300-1000 µT
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Electrified railways
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Up to 100 µT
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Typical 500 kV DC transmission line (within the right-of-way)
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10-57 µT
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It does not mention the distance of measurement, but it does give a good picture the amount of magnetic fields around your environment.
Is low frequency EMF harmful?
Quote from WHO:
The absence of health effects could mean that there really are none; however, it could also signify that an existing effect is undetectable with present methods.
Results of diverse studies (cellular, animal, and epidemiology) must be considered together before drawing conclusions about possible health risks of a suspected environmental hazard. Consistent evidence from these very different types of studies increases the degree of certainty about a true effect.
Static electric and magnetic fields associated with DC transmission lines are not viewed as a health concern.
Their levels are very low and similar to the naturally occurring static fields we are exposed to in our daily lives. Static electric fields cannot penetrate animal or plant tissues; they can only create a static charge on the surface.
The bulk of scientific research on electric and magnetic fields has focused on AC or higher frequency fields generated by microwave communications and X-rays. Their characteristics are very different from those of static fields.The International Commission on Electromagnetic Safety, which has one of the lowest levels for public exposure, recommends a public exposure guideline of 1,180,000 mG. By comparison, the static magnetic field produced by a typical 500 kV DC line is estimated at up to 570 mG directly beneath the line.
Health Canada, the World Health Organization (WHO) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) evaluate and report on public and occupational health issues using comprehensive and unbiased weight-of-evidence reviews of the research available. Their reviews have concluded that the risk to human health from static electric and magnetic fields produced by DC lines is very low.
During the 1990s, most EMF research focused on extremely low frequency exposures stemming from conventional power sources, such as power lines, electrical substations, or home appliances. While some of these studies showed a possible link between EMF field strength and an increased risk for childhood leukemia, their findings indicated that such an association was weak.
Now, in the age of cellular telephones, wireless routers, and portable GPS devices (all known sources of EMF radiation), concerns regarding a possible connection between EMFs and adverse health effects still persists, though
current research continues to point to the same weak association.
Additionally, the few studies that have been conducted on adults show no evidence of a link between EMF exposure and adult cancers, such as leukemia, brain cancer, and breast cancer. Nevertheless, NIEHS recommends continued education on practical ways of reducing exposures to EMFs.
Quote from Japan EMF Information Center:
WHO Fact Sheet No. 296 (Electromagnetic hypersensitivity, EHS) reports that "the symptoms most commonly experienced include dermatological symptoms (redness, tingling, and burning sensations) as well as neurasthenic and vegetative symptoms (fatigue, tiredness, concentration difficulties, dizziness, nausea, heart palpitations, and digestive disturbances)." Some people allege that such symptoms are related to EMF exposure.
Summaries:
- Electric fields are not a concern as it cannot penetrate animal or plant tissues.
- The further from the source the smaller the field strength and its effect.
- Low frequency (AC) EMF fields are riskier than static (DC) EMF fields.
- There is no evidence to link health risk to EMF; at the same time there is no evidence to prove EMF does not has health risk!! Thus, NIEHS recommends continued education on practical ways of reducing exposures to EMFs.
- Electromagnetic hypersensitivity (EHS), do you have it?
What do the car manufacturers say about EMF of their Hybrid car? Is there any independent organization measure EMF in Hybrid car?
